U.S. patent application number 13/514418 was filed with the patent office on 2012-12-20 for selective beta-glucuronidase inhibitors as a treatment for side effects of camptothecin antineoplastic agents.
This patent application is currently assigned to THE UNIVERSITY OF NORTH CAROLINA AT CHAPEL HILL. Invention is credited to Kimberly Terry Lane, Sridhar Mani, Matthew R. Redinbo, John Scott, Bret David Wallace, Alfred Williams, Li-An Yeh.
Application Number | 20120322797 13/514418 |
Document ID | / |
Family ID | 44145914 |
Filed Date | 2012-12-20 |
United States Patent
Application |
20120322797 |
Kind Code |
A1 |
Redinbo; Matthew R. ; et
al. |
December 20, 2012 |
SELECTIVE BETA-GLUCURONIDASE INHIBITORS AS A TREATMENT FOR SIDE
EFFECTS OF CAMPTOTHECIN ANTINEOPLASTIC AGENTS
Abstract
Compounds, compositions and methods are provided that comprise
selective .beta.-glucuronidase inhibitors for both aerobic and
anaerobic bacteria, especially enteric bacteria normally associated
with the gastrointestinal tract. The compounds, compositions and
methods can be for inhibiting bacterial .beta.-glucuronidases and
for improving efficacy of camptothecin-derived antineoplastic
agents or glucuronidase-substrate agents or compounds by
attenuating the side effects caused by reactivation by bacterial
.beta.-glucuronidases of glucuronidated metabolites of
camptothecin-derived antineoplastic agents or
glucuronidase-substrate agents or compounds.
Inventors: |
Redinbo; Matthew R.;
(Durham, NC) ; Mani; Sridhar; (Riverdale, NY)
; Williams; Alfred; (Durham, NC) ; Scott;
John; (Durham, NC) ; Yeh; Li-An; (Cary,
NC) ; Wallace; Bret David; (Chapel Hill, NC) ;
Lane; Kimberly Terry; (Christiansburg, VA) |
Assignee: |
THE UNIVERSITY OF NORTH CAROLINA AT
CHAPEL HILL
Chapel Hill
NC
NORTH CAROLINA CENTRAL UNIVERSITY
Durham
NC
ALBERT EINSTEIN COLLEGE OF MEDICINE OF YESHIVA
UNIVERSITY
Bronx
NY
|
Family ID: |
44145914 |
Appl. No.: |
13/514418 |
Filed: |
December 9, 2010 |
PCT Filed: |
December 9, 2010 |
PCT NO: |
PCT/US10/59690 |
371 Date: |
August 27, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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61285265 |
Dec 10, 2009 |
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61408032 |
Oct 29, 2010 |
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Current U.S.
Class: |
514/232.8 ;
514/252.16; 514/254.11; 514/312; 514/447; 544/112; 544/278;
544/281; 544/377; 546/157; 549/68 |
Current CPC
Class: |
A61K 31/5377 20130101;
A61K 31/496 20130101; A61P 31/04 20180101; A61K 31/435 20130101;
A61K 31/496 20130101; A61P 35/00 20180101; C07D 317/50 20130101;
A61K 31/4704 20130101; A61K 45/06 20130101; A61K 31/435 20130101;
C07D 495/04 20130101; A61K 31/4745 20130101; A61K 31/519 20130101;
A61K 31/5377 20130101; C07D 333/38 20130101; C07D 215/227 20130101;
A61K 31/4745 20130101; A61K 31/519 20130101; A61K 31/381 20130101;
A61P 1/00 20180101; C07D 487/04 20130101; A61K 31/4704 20130101;
A61K 31/38 20130101; A61K 2300/00 20130101; A61K 31/335 20130101;
A61K 2300/00 20130101; A61K 2300/00 20130101; A61K 2300/00
20130101; A61K 2300/00 20130101; A61K 2300/00 20130101; A61K
2300/00 20130101; A61K 2300/00 20130101; A61K 31/00 20130101; A61K
2300/00 20130101; A61K 31/38 20130101; A61K 31/381 20130101; C07D
495/14 20130101; A61P 1/12 20180101; A61K 31/335 20130101 |
Class at
Publication: |
514/232.8 ;
546/157; 514/312; 549/68; 514/447; 544/278; 514/252.16; 544/281;
544/377; 514/254.11; 544/112 |
International
Class: |
A61K 31/4704 20060101
A61K031/4704; A61P 31/04 20060101 A61P031/04; C07D 333/38 20060101
C07D333/38; A61K 31/381 20060101 A61K031/381; A61K 31/5377 20060101
A61K031/5377; A61K 31/496 20060101 A61K031/496; C07D 487/04
20060101 C07D487/04; C07D 405/10 20060101 C07D405/10; C07D 495/14
20060101 C07D495/14; C07D 215/227 20060101 C07D215/227; C07D 495/04
20060101 C07D495/04 |
Claims
1. A compound having selective .beta.-glucuronidase inhibitor
activity, the compound selected from the group consisting of:
##STR00012## ##STR00013## and active derivatives thereof.
2. A composition comprising at least one compound of claim 1.
3. The composition of claim 2 further comprising a pharmaceutically
acceptable carrier.
4. The composition of claim 2 wherein said composition is
administered prior to, concurrently with, or after the
administration of at least one camptothecin-derived antineoplastic
agent.
5. The composition of claim 4, wherein at least one
camptothecin-derived antineoplastic agent is selected from the
group consisting of camptothecin, diflomotecan, exatecan,
gimatecan, irinotecan, karenitecin, lurtotecan, rubitecan,
silatecan and topotecan.
6. The composition of claim 2, wherein the at least one selective
.beta.-glucuronidase inhibitor is at a concentration from about 1
nM to about 1 mM.
7. A method for selectively inhibiting bacterial
.beta.-glucuronidases, the method comprising administering to a
subject in need thereof an effective amount of at least one
selective .beta.-glucuronidase inhibitor.
8. The method of claim 7, wherein the at least one selective
.beta.-glucuronidase inhibitor is selected from the following
compounds: ##STR00014## ##STR00015## and active derivatives
thereof.
9. The method of claim 8, wherein the at least one selective
.beta.-glucuronidase inhibitor is administered to the subject at a
concentration from about 1 nM to about 1 mM.
10. The method of claim 7, wherein the bacterial
.beta.-glucuronidases are enteric bacterial
.beta.-glucuronidases.
11. The method of claim 10, wherein the bacteria are selected from
the group consisting of a Bacteroides sp., Bifidobacterium sp.,
Catenabacterium sp., Clostridium sp., Corynebacterium sp.,
Enterococcus faecalis, Enterobacteriaceae, Lactobacillus sp.,
Peptostreptococcus sp., Propionibacterium sp., Proteus sp.,
Mycobacterium sp., Pseudomonas sp., Staphylococcus sp. and
Streptococcus sp.
12. A method for improving camptothecin-derived antineoplastic
agent efficiency, the method comprising administering to a subject
prior to, concurrently with or after administration of a
camptothecin-derived antineoplastic agent a therapeutically
effective amount of at least one selective .beta.-glucuronidase
inhibitor.
13. A method for attenuating side effects in a subject being
administered a camptothecin-derived antineoplastic agent, the
method comprising administering prior to, concurrently with or
after administration of a camptothecin-derived antineoplastic agent
a therapeutically effective amount of at least one selective
.beta.-glucuronidase inhibitor.
14. The method of claim 12, wherein the at least one selective
.beta.-glucuronidase inhibitor is selected from the compounds of
embodiment 1.
15. The method of claim 12, wherein the camptothecin-derived
antineoplastic agent is selected from the group consisting of
camptothecin, diflomotecan, exatecan, gimatecan, irinotecan,
karenitecin, lurtotecan, rubitecan, silatecan and topotecan.
16. The method of claim 15, wherein the camptothecin-derived
antineoplastic agent is irinotecan.
17. A method to alleviate gastrointestinal distress associated with
chemotherapy comprising: a) administering to an animal an
anti-cancer effective amount of a chemotherapeutic agent, and b)
administering to the same animal an inhibitory effective amount of
a glucuronidase inhibitor.
18. The method of claim 17, wherein the chemotherapeutic active
agent is a camptothecin-derived antineoplastic agent.
19. The method of claim 17, wherein the .beta.-glucuronidase
inhibitor is selected from the group consisting of: ##STR00016##
##STR00017## and active derivatives thereof.
20. A method for improving the efficiency of a
glucuronidase-substrate agent or compound, the method comprising
administering to a subject prior to, concurrently with or after
administration of said agent or compound a therapeutically
effective amount of at least one selective .beta.-glucuronidase
inhibitor.
21. The method of claim 20, wherein said selective
.beta.-glucuronidase inhibitor is selected from the group
consisting of: ##STR00018## ##STR00019## and active derivatives
thereof.
Description
FIELD OF THE INVENTION
[0001] The invention relates generally to compositions and methods
for inhibiting enteric bacterial enzymes and for attenuating side
effects of antineoplastic agents, and more particularly to
compositions and methods for inhibiting bacterial
.beta.-glucuronidases and for attenuating side effects of
camptothecin-derived antineoplastic agents or
glucuronidase-substrate agents or compounds used in the treatment
of various neoplasms or other conditions.
BACKGROUND
[0002] Camptothecin, a plant alkaloid derived from the Chinese
Camptotheca acuminata tree, was added to the National Cancer
Institute's natural products screening set in 1966. It showed not
only strong antineoplastic activity, but also poor bioavailability
and toxic side effects. After thirty years of modifying the
camptothecin scaffold, two camptothecin derivatives emerged and are
now approved for clinical use. The first derivative is topotecan
(also called Hycamptin.RTM.; GlaxoSmithKline; London, England),
which can be used to treat solid brain, lung and ovarian tumors.
The second derivative is irinotecan (also called CPT-11 and
Camptosar.RTM.; Pfizer; New York City, N.Y.), which can be used to
treat solid brain, colon and lung tumors, as well as refractory
forms of leukemia and lymphoma.
[0003] The sole target of camptothecin and camptothecin-derived
antineoplastic agents is human topoisomerase I. Camptothecin and
camptothecin-derived antineoplastic agents bind to covalent
topoisomerase I-DNA complexes and prevent re-ligation of broken
single DNA strands, effectively trapping it on the DNA. Such
immobilized macromolecular adducts act as roadblocks to the
progression of DNA replication and transcription complexes, causing
double-strand DNA breaks and apoptosis. Structural studies have
established that camptothecin and other camptothecin-derived
antineoplastic agents stack into duplex DNA, replacing the base
pair adjacent to the covalent phosphotyrosine linkage. See,
Chrencik et al. (2004) J. Mol. Biol. 339:773-784; and Staker et al.
(2002) Proc. Natl. Acad. Sci. USA 99:15387-15392. Re-ligation of
the nicked DNA strand is prevented by increasing the distance
between the 5'-hydroxyl and the 3'-phosphotyrosine linkage to
>11 .ANG.. Because neoplastic cells grow rapidly, camptothecin
and other camptothecin-derived antineoplastic agents impact these
cells more significantly than normal cells and tissues.
[0004] Camptothecin-derived antineoplastic agent efficacy,
including that of camptothecin, is limited by a delayed diarrhea
that follows its administration by about two to four days. For
example, "reactivation" of SN-38G, a glucuronidated inactive
metabolite of irinotecan, to SN-38, its active metabolite, by
.beta.-glucuronidases of enteric bacteria kills intestinal
epithelial cells and causes a dose-limiting diarrhea. See, e.g.,
Matsui et al. (2003) Surg. Oncol. Clin. N. Am. 12:795-811; and
Tobin et al. (2003) Oncol. Rep. 10:1977-1979.
[0005] While broad-spectrum antibiotics have been used to eliminate
enteric bacteria from the gastrointestinal tract prior to
irinotecan treatment to reduce reactivation, this approach has
several drawbacks. First, enteric bacteria (i.e., normal flora)
play essential roles in carbohydrate metabolism, vitamin production
and the processing of bile acids, sterols and xenobiotics. Thus, a
partial or complete removal of enteric bacteria is not ideal for
subjects already challenged by neoplastic growths and chemotherapy.
Second, the elimination of the symbiotic enteric bacteria from even
healthy subjects significantly increases risk of infection by
pathogenic bacteria, including enterohemorrhagic Escherichia coli
and Clostridium difficile. Third, bacterial antibiotic resistance
is a human health crisis, and the unnecessary use of antibiotcs is
a significant contributor to this crisis.
[0006] Likewise, weak/non-selective .beta.-glucuronidase inhibitors
such as saccharic acid 1,4-lactone can be administered to reduce
reactivation. These inhibitors, however, are only partially
effective in preventing reactivation of glucuronidated metabolites
of camptothecin and other camptothecin-derived antineoplastic
agents. Fittkau et al. (2004) J. Cancer Res. Clin. Oncol.
130:388-394. Additional non-specific inhibitors of
.beta.-glucuronidase include certain divalent cations (e.g.,
Cu.sup.2+ and Zn.sup.2+), galacturonic acid and glucuronic acid.
Naleway, "Histochemical, spectrophotometric, and fluorometric GUS
substrates" 61-76 In: GUS Protocols: Using the GUS Gene as a
Reporter of Gene Expression (Gallagher ed., Academic Press 1992);
and Handbook of Enzyme Inhibitors, Part A (Zollner ed., 2.sup.nd
ed. 1993).
[0007] For the foregoing reasons, there is a need for alternative
compositions and methods for inhibiting bacterial
.beta.-glucuronidases and for attenuating reactivation of
glucuronidated metabolites of camptothecin and other
camptothecin-derived antineoplastic agents or any other
glucuronidase-substrate agents or compounds.
BRIEF SUMMARY
[0008] Compositions and methods are provided for selectively
inhibiting bacterial .beta.-glucuronidases. Accordingly,
compositions of the present invention include .beta.-glucuronidase
inhibiting agents that selectively inhibit bacterial
.beta.-glucuronidases from hydrolyzing glucuronides. The
selectively inhibiting agents can be provided as formulated
compositions and can be administered to subjects in need thereof.
In particular, the selectively inhibiting agents or compositions
comprising such agents can be administered prior to, concurrently
with or after an antineoplastic agent, particularly a
camptothecin-derived antineoplastic agent, to treat a variety of
neoplasms including cancers, or in the same manner can be used with
any other glucuronidase-substrate agent(s) or compound(s). When
used together, the selectively inhibiting agent reduces side
effects of antineoplastic agents or any other
glucuronidase-substrate agent(s) or compound(s), thus improving
efficacy of the antineoplastic agent or other agents.
[0009] The selectively inhibiting agents and compositions can be
used in methods for treating cancer and for reducing side effects
of antineoplastic agents, such as camptothecin-derived
antineoplastic agents. Thus, the gastrointestinal distress that
typically accompanies treatment with an antineoplastic agent can be
attenuated. The methods are also useful for attenuating or
improving any adverse reactions associated with administration of
glucuronidase-substrate agent(s) or compound(s).
[0010] Methods of the present invention include administering to a
subject in need thereof a therapeutically effective amount of at
least one .beta.-glucuronidase inhibiting agent that selectively
inhibits bacterial .beta.-glucuronidases from hydrolyzing
glucuronides.
[0011] The present invention provides the first potent, selective
inhibitors of bacterial .beta.-glucuronidases in both aerobic and
anaerobic bacteria associated with the gastrointestinal tract.
[0012] The following embodiments are encompassed by the present
invention.
[0013] 1. A compound having selective .beta.-glucuronidase
inhibitor activity, the compound selected from the group consisting
of:
##STR00001## ##STR00002##
and active derivatives thereof.
[0014] 2. A composition comprising at least one compound selected
from the group consisting of the compounds of embodiment 1.
[0015] 3. The composition of embodiment 2 further comprising a
pharmaceutically acceptable carrier.
[0016] 4. The composition of embodiment 2 or 3 wherein said
composition is administered prior to, concurrently with, or after
the administration of at least one camptothecin-derived
antineoplastic agent.
[0017] 5. The composition of embodiment 4, wherein at least one
camptothecin-derived antineoplastic agent is selected from the
group consisting of camptothecin, diflomotecan, exatecan,
gimatecan, irinotecan, karenitecin, lurtotecan, rubitecan,
silatecan and topotecan.
[0018] 6. The composition of any of embodiments 2-5, wherein the at
least one selective .beta.-glucuronidase inhibitor is at a
concentration from about 1 nM to about 1 mM.
[0019] 7. A method for selectively inhibiting bacterial
.beta.-glucuronidases, the method comprising administering to a
subject in need thereof an effective amount of at least one
selective .beta.-glucuronidase inhibitor.
[0020] 8. The method of embodiment 7, wherein the at least one
selective .beta.-glucuronidase inhibitor is selected from the
compounds of embodiment 1.
[0021] 9. The method of embodiment 8, wherein the at least one
selective .beta.-glucuronidase inhibitor is administered to the
subject at a concentration from about 1 nM to about 1 mM.
[0022] 10. The method of embodiment 7, wherein the bacterial
.beta.-glucuronidases are enteric bacterial
.beta.-glucuronidases.
[0023] 11. The method of embodiment 10, wherein the bacteria are
selected from the group consisting of a Bacteroides sp.,
Bifidobacterium sp., Catenabacterium sp., Clostridium sp.,
Corynebacterium sp., Enterococcus faecalis, Enterobacteriaceae,
Lactobacillus sp., Peptostreptococcus sp., Propionibacterium sp.,
Proteus sp., Mycobacterium sp., Pseudomonas sp., Staphylococcus sp.
and Streptococcus sp.
[0024] 12. A method for improving camptothecin-derived
antineoplastic agent efficiency, the method comprising
administering to a subject prior to, concurrently with or after
administration of a camptothecin-derived antineoplastic agent a
therapeutically effective amount of at least one selective
.beta.-glucuronidase inhibitor.
[0025] 13. A method for attenuating side effects in a subject being
administered a camptothecin-derived antineoplastic agent, the
method comprising administering prior to, concurrently with or
after administration of a camptothecin-derived antineoplastic agent
a therapeutically effective amount of at least one selective
.beta.-glucuronidase inhibitor.
[0026] 14. The method of embodiment 12 or 13, wherein the at least
one selective .beta.-glucuronidase inhibitor is selected from the
compounds of embodiment 1.
[0027] 15. The method of embodiment 12 or 13, wherein the
camptothecin-derived antineoplastic agent is selected from the
group consisting of camptothecin, diflomotecan, exatecan,
gimatecan, irinotecan, karenitecin, lurtotecan, rubitecan,
silatecan and topotecan.
[0028] 16. The method of embodiment 15, wherein the
camptothecin-derived antineoplastic agent is irinotecan.
[0029] 17. A method to alleviate gastrointestinal distress
associated with chemotherapy comprising: [0030] a) administering to
an animal an anti-cancer effective amount of a chemotherapeutic
agent, and [0031] b) administering to the same animal an inhibitory
effective amount of a .beta.-glucuronidase inhibitor.
[0032] 18. The method of embodiment 17, wherein the
chemotherapeutic active agent is a camptothecin-derived
antineoplastic agent.
[0033] 19. The method of embodiment 17, wherein the
.beta.-glucuronidase inhibitor is selected from the group
consisting of:
##STR00003## ##STR00004##
and active derivatives thereof.
[0034] 20. A method for improving the efficiency of a
glucuronidase-substrate agent or compound, the method comprising
administering to a subject prior to, concurrently with or after
administration of said agent or compound a therapeutically
effective amount of at least one selective .beta.-glucuronidase
inhibitor.
[0035] 21. The method of embodiment 20, wherein said selective
.beta.-glucuronidase inhibitor is selected from the group
consisting of:
##STR00005## ##STR00006##
and active derivatives thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] The present invention will be better understood and
features, aspects and advantages other than those set forth above
will become apparent when consideration is given to the following
detailed description thereof. Such detailed description makes
reference to the following drawings, wherein:
[0037] FIG. 1A shows a diagram of the activation and metabolism of
irinotecan.
[0038] FIG. 1B shows the structure of irinotecan, as well as its
active (SN-38) and inactive (SN-38G) metabolites.
[0039] FIG. 2A shows a three-dimensional image of an E. coli
.beta.-glucuronidase dimer and tetramer. FIG. 2B shows a
crystallographic image of an E. coli .beta.-glucuronidase tetramer
in its active form.
[0040] FIG. 3A shows an illustration of a native crystal structure
of E. coli .beta.-glucuronidase in which the active site is
occluded by a loop (top image), and an image of a
glucaro-.delta.-lactam (GDL)-bound E. coli .beta.-glucuronidase in
which the loop shifted (bottom image). FIG. 3B shows a graphic
representation of the loop shifting at the active site.
[0041] FIG. 4A shows a structure of each of the nine selective
.beta.-glucuronidase inhibitors described herein. FIG. 4B shows a
graph depicting a reduction in absorbance that represents
decreasing .beta.-glucuronidase with an increase in
.beta.-glucuronidase inhibitor concentration (inhibitor 9) of E.
coli .beta.-glucuronidase (left bar at each concentration) compared
to bovine .beta.-glucuronidase (right bar at each concentration)
(abscissa is inhibitor concentration in mM; ordinate is relative
absorbance). FIG. 4C shows a graph depicting a significant effect
of the selective .beta.-glucuronidase inhibitors on
.beta.-glucuronidase activity of E. coli under anaerobic (left bar
at each treatment) and aerobic (right bar at each treatment)
conditions (abscissa is treatment condition; ordinate is relative
absorbance). FIG. 4D shows a graph depicting efficacy of the
selective .beta.-glucuronidase inhibitors on the obligate anaerobe
Bacteroides vulgatus (abscissa is treatment condition; ordinate is
relative absorbance).
[0042] FIG. 5 shows a superimposed image of E. coli
.beta.-glucuronidase and Homo sapiens .beta.-glucuronidase.
[0043] FIG. 6 shows an alignment of primary .beta.-glucuronidase
sequences from E. coli (see SEQ ID NO: 1) and H. sapiens (see SEQ
ID NO: 2).
[0044] FIG. 7 shows an illustration of residues of interest for the
interaction of GDL with the active site of
.beta.-glucuronidase.
[0045] FIG. 8 shows a modeling of the shift in the active site of
.beta.-glucuronidase.
[0046] FIG. 9 shows illustrations of various substrates for
.beta.-glucuronidase assays.
[0047] FIG. 10 shows a graph depicting a reduction in absorbance of
mutant E. coli lacking .beta.-glucuronidase or a mutant E. coli
having a vector encoding for .beta.-glucuronidase compared to
wild-type E. coli (left bar is 0 mM IPTG; right bar is 0.3 mM IPTG)
(abscissa is E. coli cell type; ordinate is relative
absorbance).
[0048] FIG. 11 shows a graph depicting a relatively weak effect of
GDL in vitro (left bar is in vitro treatment; right bar is in vivo
treatment) (abscissa is GDL concentration (mM); ordinate is
relative absorbance).
[0049] FIG. 12 shows a graph depicting a lack of significant effect
of the selective .beta.-glucuronidase inhibitors on viability/cell
survival of E. coli (abscissa is treatment condition; ordinate is
colony forming units).
[0050] FIG. 13 shows a graph depicting a lack of cytotoxicity of
the selective .beta.-glucuronidase inhibitors on human colonic
cells (abscissa is treatment condition; ordinate is relative
fluorescence signal).
[0051] FIG. 14A shows illustration of an E. coli
.beta.-glucuronidase in which the active site is bound to SN-38G.
FIG. 14B shows a structural representation of FIG. 14A. FIG. 14C
shows an illustration an E. coli .beta.-glucuronidase in which the
active site is bound to inhibitor 9. FIG. 14D shows a structural
representation of FIG. 14C.
[0052] While the present invention is susceptible to various
modifications and alternative forms, exemplary embodiments thereof
are shown by way of example in the drawings and are herein
described in detail. It should be understood, however, that the
description of exemplary embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION
[0053] Overview
[0054] The present invention relates to an identification of potent
(i.e., low uM to high pM), selective .beta.-glucuronidase
inhibitors for both aerobic and anaerobic bacteria, especially
those bacteria associated with the gastrointestinal tract (i.e.,
enteric bacteria). The present invention therefore includes
compositions and methods for inhibiting bacterial
.beta.-glucuronidases and for improving efficacy of
camptothecin-derived antineoplastic agents or
glucuronidase-substrate agents or compounds by attenuating the
gastrointestinal distress caused by reactivation of glucuronidated
metabolites of such agents.
[0055] Compounds of interest herein include:
##STR00007## ##STR00008##
and active derivatives thereof.
[0056] As used herein, "active derivative" and the like means a
modified .beta.-glucuronidase inhibiting compound that retains an
ability to selectively inhibit bacterial .beta.-glucuronidases. For
example, the derivative can be capable of inhibiting
.beta.-glucuronidase reactivation of SN-38G to SN-38, but not
killing bacteria that inhabit the gastrointestinal tract or
inhibiting mammalian .beta.-glucuronidases. One of skill in the art
is familiar with assays for testing the ability of an active
derivative compound for selectively inhibiting
.beta.-glucuronidases with no toxicity to the bacteria that inhabit
the gastrointestinal tract. See, Experimental section below.
[0057] As used herein, "inhibit," "inhibiting" and the like means
that .beta.-glucuronidase expression, activity or function and
therefore metabolite reactivation can be reduced in a subject.
Likewise, "attenuate" means to reduce or lessen. That is, the
.beta.-glucuronidase activity can be reduced. Likewise, the side
effects of a chemotherapeutic agent can be reduced. Thus, to
inhibit or attenuate means a reduction of at least about 5%, about
10%, about 15%, about 20%, about 25%, about 30%, about 35%, about
40%, about 45%, about 50%, about 55%, about 60%, about 65%, about
70%, about 75%, about 80%, about 85%, about 90%, about 95% or up to
about 100% as compared to an appropriate control.
[0058] As used herein, "selectively inhibit" and the like means
that a .beta.-glucuronidase inhibitor reduces bacterial, but not
mammalian, .beta.-glucuronidase activity. That is, the
.beta.-glucuronidase inhibitor can bind to and can prevent
bacterial, but not mammalian, .beta.-glucuronidases from
hydrolyzing glucuronides.
[0059] As used herein, ".beta.-glucuronidase" and the like means an
enzyme (EC 3.2.1.31) capable of hydrolyzing .beta.-glucuronides,
but not .alpha.-glucuronides or .beta.-glucosides. See, Basinska
& Florianczyk (2003) Ann. Univ. Mariae Curie Sklodowska Med.
58:386-389; Miles et al. (1955) J. Biol. Chem. 217:921-930. As used
herein, a "glucuronide" and the like means a substance produced by
linking glucuronic acid to another substance via a glycosidic bond.
Examples of glucuronides of interest herein include, but are not
limited to, glucuronides of camptothecin-derived antineoplastic
agents such as SN-38G (7-ethyl-10-hydroxycamptothecin
glucuronide).
[0060] As used herein, "camptothecin-derived antineoplastic agent"
and the like means a cytotoxic quinoline alkaloid that inhibits the
DNA enzyme topoisomerase I. A camptothecin-derived antineoplastic
agent can include a structure comprising at least the
following:
##STR00009##
[0061] Camptothecin-derived antineoplastic agents include, but are
not limited to, camptothecin (i.e.,
(S)-4-ethyl-4-hydroxy-1H-pyrano[3',4':6,7]indolizino[1,2-b]quinoline-3,14-
-(4H,12H)-dione); diflomotecan (i.e.,
(5R)-5-ethyl-9,10-difluoro-1,4,5,13-tetrahydro-5-hydroxy-3H,15H-oxepino[3-
',4':6,7]indolizino[1,2-b]quinoline-3,15-dione); exatecan (i.e.,
(1S,9
S)-1-amino-9-ethyl-5-fluoro-1,2,3,9,12,15-hexahydro-9-hydroxy-4-methyl-10-
H,13H-benzo(de)pyrano(3',4':6,7)indolizino(1,2-b)quinoline-10,13-dione);
gimatecan (i.e.,
(4S)-11-((E)-((1,1-dimethylethoxy)imino)methyl)-4-ethyl-4-hydroxy-1,12-di-
hydro-14H-pyrano(3',4':6,7)indolizino(1,2-b)quinoline-3,14(4H)-dione);
irinotecan (i.e.,
(S)-4,11-diethyl-3,4,12,14-tetrahydro-4-hydroxy-3,14-dioxo1H-pyrano[3',4'-
:6,7]-indolizino[1,2-b]quinolin-9-yl-[1,4'bipiperidine]-1'-carboxylate);
karenitecin (i.e.,
(4S)-4-ethyl-4-hydroxy-11-(2-trimethylsilyl)ethyl)-1H-pyrano[3',4':6,7]in-
dolizino[1,2-b]quinoline-3,14(4H,12H)-dione); lurtotecan (i.e.,
7-(4-methylpiperazinomethylene)-10,11-ethylenedioxy-20(S)-camptothecin);
rubitecan (i.e.,
(4S)-4-ethyl-4-hydroxy-10-nitro-1H-pyrano[3',4':6,7]indolizino[1,2-b]quin-
oline-3,14(4H,12H)-dione); silatecan (i.e.,
7-tert-butyldimethylsilyl-10-hydroxycamptothecin); and topotecan
(i.e.,
(S)-10-[(dimethylamino)methyl]-4-ethyl-4,9-dihydroxy-1H-pyrano[3',4':6,7]-
indolizino[1,2-b]quinoline-3,14(4H,12H)-dione).
[0062] Of interest herein is irinotecan (CPT-11 or Camptosan.RTM.),
which is a potent camptothecin-derived antineoplastic agent for
treating solid malignancies of the brain, colon and lung, as well
as refractory forms of leukemia and lymphoma. Irinotecan is a
prodrug that must be converted into its active form, SN-38
(7-ethyl-10-hydroxy-camptothecin), to have antineoplastic activity.
During its excretion, SN-38 is glucuronidated to SN-38 glucuronide
(SN-38G) by phase II drug metabolizing
UDP-glucuronosyltranserases.
[0063] The term "glucuronidase-substrate agent(s) or compound(s)"
refers to any drug, agent or compound or, in particular, a
metabolite thereof that can be a substrate for glucuronidase. Thus,
in some instances, a drug, compound or agent that is not itself a
substrate, but is metabolized to a substrate is encompassed by the
term as used herein. Any drug, compound or agent or metabolite
thereof that is glucuronidated, also referred to as glucuronides,
can be a substrate for glucuronidase and is also described herein
as glucuronidase-substrate agent(s) or compound(s). Many drugs,
agents or compounds undergo glucuronidation at some point in their
metabolism. Alternatively, the drug, agent or compound may be a
glucuronide pro-drug. These glucuronides may have different
properties than the parent drug, agent or compound. Glucuronidation
can modulate the potency of some drugs: the 6-glucuronide of
morphine is a more potent analgesic than the parent compound,
whereas the 3-glucuronide is a morphine antagonist. In addition,
steroid glucuronidation can produce more active or toxic
metabolites under pathophysiological conditions or during steroid
therapies.
[0064] Drugs, agents or compounds or metabolites thereof which are
substrates for glucuronidase can have their respective properties
altered by glucuronidase hydrolysis. In a specific, non-limiting
example, if the drug, agent, compound or metabolite thereof has
been metabolized to a glucuronide, the hydrolysis of the
glucuronide can reactivate the drug, agent, compound or metabolite
thereof. In many cases, this reactivation can cause adverse
reactions. For example, if a glucuronide drug, agent or compound or
metabolite thereof is present in the gut, glucuronidase hydrolysis
in the gut can lead to gastrointestinal distress.
[0065] The methods described herein are useful for attenuating,
ameliorating or improving the adverse reactions, such as
gastrointestinal distress, caused by the action of glucuronidase on
a drug, agent or compound or, in particular, a metabolite thereof.
As described fully elsewhere herein, hydrolysis of glucuronides can
lead to adverse reactions. The methods described herein inhibit or
decrease the activity of .beta.-glucuronidases. The methods can
therefore be useful to attenuate, ameliorate or improve adverse
reactions, such as gastrointestinal distress, associated with
administering such drugs, agents or compounds. The methods can also
improve the tolerance of any such drug, agent or compound or
metabolite thereof that can form a glucuronide. As such,
administration of a glucuronidase inhibitor can rescue or improve a
treatment with any drug, agent or compound, wherein glucuronidase
hydrolysis of a glucuronide related to the drug, agent, compound or
metabolite thereof is causing one or more adverse reactions,
particularly gastrointestinal distress or toxicity. Patient
compliance and outlook would also improve with the lessening of
adverse reactions.
[0066] Reactivation of inactive metabolites such as SN-38G to
active SN-38 occurs in the gastrointestinal tract and results from
bacterial .beta.-glucuronidases. As noted above, the reactivated
metabolites can lead to a gastrointestinal distress such as
diarrhea, which often can be a dose-limiting side effect of the
cancer therapy or the therapy to treat any other conditions. As
used herein, "dose-limiting" indicates that the side effect from
administration of a camptothecin-derived antineoplastic agent or
glucuronidase-substrate agents or compounds prevents a subject in
need of cancer therapy or therapy to treat any other conditions
from receiving a recommended amount. As increasing amounts of the
camptothecin-derived antineoplastic agent or
glucuronidase-substrate agents or compounds are administered to a
subject, increased amounts of glucuronidated metabolites are
therefore available as a substrate for the bacterial
.beta.-glucuronidases. The resulting reactivated metabolites not
only adversely affect a subject's well-being by causing serious
side effects, particularly gastrointestinal distress, but also
impair treatment outcome by limiting the amount of the
camptothecin-derived antineoplastic agent or
glucuronidase-substrate agents or compounds that can be
administered to the subject.
[0067] The selective .beta.-glucuronidase inhibiting compounds,
compositions, and methods of use thereof described herein are
useful in a variety of applications. For example, the compounds,
compositions and methods disclosed herein can be used for
discovering additional selective .beta.-glucuronidase inhibitors in
a screening assay as controls in which potential selective
.beta.-glucuronidase inhibitors can be compared.
[0068] The selective .beta.-glucuronidase inhibiting compounds,
compositions and methods of use thereof also can be used to improve
efficacy of camptothecin-derived antineoplastic agents or
glucuronidase-substrate agents or compounds by attenuating the side
effects associated with their administration during the treatment
of various neoplasms or other conditions. As used herein,
"neoplasm" and the like means an abnormal growth of cells or a mass
of tissue resulting from an abnormal proliferation of cells.
Neoplasms frequently result in a lump or tumor and can be benign,
pre-malignant (i.e., pre-cancerous) or malignant (i.e., cancerous
growths including primary or metastatic cancerous growths).
"Neoplastic" means of or related to a neoplasm. Thus, the selective
.beta.-glucuronidase inhibiting compounds and compositions can be
used to improve treatment of a variety of neoplasms including, but
not limited to, neoplasms of the bone, brain, breast, cervix,
colon, intestines, kidney, liver, lung, pancreatic, prostate,
rectum, stomach, throat, uterus, and the like. The term
"conditions" refers to any disease or disorder for which the
glucuronidase-substrate agents or compounds are being primarily
administered.
[0069] Compositions
[0070] The present invention provides compounds and compositions
for selectively inhibiting bacterial .beta.-glucuronidases. The
compounds and compositions can include an effective amount of at
least one selective .beta.-glucuronidase inhibitor selected from
the inhibitors described herein. As used herein, "effective amount"
and the like means that amount of an inhibitor or other therapeutic
agent that will elicit a biological or medical response of a cell,
tissue, system or animal that is being sought, for instance, by a
researcher or clinician. That is, the effective amount of a
selective .beta.-glucuronidase inhibitor or composition thereof is
an amount sufficient to reduce or attenuate side effects of
camptothecin-derived antineoplastic agents or
glucuronidase-substrate agents or compounds. Particularly, the
effective amount is that amount of the selective
.beta.-glucuronidase inhibitor or composition thereof to attenuate
the side effects in a subjected being treated with a
camptothecin-derived antineoplastic agent or
glucuronidase-substrate agents or compounds. More particularly, the
effective amount is that amount sufficient to inhibit reactivation
of glucuronidated metabolites such as SN-38G to SN-38. For example,
the effective amount of the selective .beta.-glucuronidase
inhibitor can be about 1 pM to about 1 mM, about 1 nM to about 1
mM, about 1 .mu.M to about 1 mM, about 1 pM to about 1 nM, about 1
nM to about 1 .mu.M, or about 1 .mu.M to about 1 mM.
[0071] As used herein, "about" means within a statistically
meaningful range of a value such as a stated concentration range,
time frame, molecular weight, volume, temperature or pH. Such a
range can be within an order of magnitude, typically within 20%,
more typically still within 10%, and even more typically within 5%
of a given value or range. The allowable variation encompassed by
"about" will depend upon the particular system under study, and can
be readily appreciated by one of skill in the art.
[0072] Examples of selective .beta.-glucuronidase inhibitors
include, but are not limited to,
##STR00010## ##STR00011##
and active derivatives thereof.
[0073] Advantageously, the .beta.-glucuronidase inhibitors
described herein are selective for bacterial .beta.-glucuronidases.
That is, the compounds inhibit .beta.-glucuronidase in bacteria but
do not have inhibitory activity toward mammalian
.beta.-glucuronidases, including human .beta.-glucuronidase. While
not intending to be bound by any particular mechanism of action,
the compounds appear to bind a .about.12 residue loop in bacterial
.beta.-glucuronidases that hovers over an active site opening. The
loop is not present in mammalian .beta.-glucuronidases, which
therefore can accommodate larger substrates and cleave glucuronic
acid moieties from long-chain glycosaminoglycans.
[0074] The .beta.-glucuronidase inhibitors exhibit other
advantages. For example, the compounds do not kill the enteric
bacteria or harm human epithelial cells, but are effective against
bacteria cultured under aerobic and anaerobic conditions.
[0075] The present invention also provides compositions comprising
the selective .beta.-glucuronidase inhibitors. The compositions can
include at least one selective .beta.-glucuronidase inhibitor
selected from the inhibitors described herein and a
pharmaceutically acceptable carrier. The compositions are
formulated to administer an effective amount to a subject in need
thereof.
[0076] As used herein, "pharmaceutically acceptable" or
"pharmacologically acceptable" means a material that is not
biologically, physiologically or otherwise undesirable to a
subject, i.e., the material may be administered to the subject in a
formulation or composition without causing any undesirable
biological effects or interacting in a deleterious manner with any
of the components of the composition in which it is contained.
[0077] The pharmaceutically acceptable carrier can be a solid or
liquid and the type can be generally chosen based on the type of
administration being used. The selective .beta.-glucuronidase
inhibitor can be administered in the form of a tablet or capsule,
as an agglomerated powder or in a liquid form. Examples of solid
carriers include, but are not limited to, lactose, sucrose, gelatin
and agar. Capsule or tablets can be easily formulated and can be
made easy to swallow or chew; other solid forms include granules,
and bulk powders. Tablets can contain suitable binders, lubricants,
diluents, disintegrating agents, coloring agents, flavoring agents,
flow-inducing agents, and melting agents.
[0078] Examples of liquid dosage forms include solutions or
suspensions in water, pharmaceutically acceptable fats or oils,
alcohols or other organic solvents, including esters, emulsion,
elixirs, syrups, solutions and/or suspensions reconstituted from
non-effervescent granules and effervescent preparations
reconstituted from effervescent granules. Such liquid dosage forms
can contain, e.g., suitable solvents, preservatives, emulsifying
agents, suspending agents, diluents, sweeteners, thickeners and
melting agents. Oral dosage forms can contain flavorants and
coloring agents.
[0079] The compositions of the invention also can include minerals
and/or vitamins such as calcium, vitamin A, vitamin B, vitamin D
and vitamin E.
[0080] Methods
[0081] The present invention provides methods for selectively
inhibiting bacterial .beta.-glucuronidases. In the methods, an
effective amount of at least one selective .beta.-glucuronidase
inhibitor can be administered to a subject in need thereof. That
is, a subject being treated with a camptothecin-derived
antineoplastic agent or glucuronidase-substrate agents or
compounds.
[0082] As used herein, "enteric bacteria" and the like mean the
normal bacteria that inhabit the human gastrointestinal track.
Examples of enteric bacteria include, but are not limited to,
Bacteroides sp. (e.g., Bateroides vulgatus), Bifidobacterium sp.
(e.g., Bifidobacterium bifidum and Bifidobacterium infantis),
Catenabacterium sp., Clostridium sp., Corynebacterium sp.,
Enterococcus sp. (e.g., Enterococcus faecalis), Enterobacteriaceae
(e.g., Escherichia coli), Lactobacillus sp., Peptostreptococcus
sp., Propionibacterium sp., Proteus sp., Mycobacterium sp.,
Pseudomonas sp. (e.g., Pseudomonas aeruginosa), Staphylococcus sp.
(e.g., Staphylococcus epidermidis and Staphylococcus aureus) and
Streptococcus sp. (e.g., Streptococcus mitis). Because enteric
bacteria commensally inhabit the gastrointestinal tract, they
promote gastrointestinal health by preventing infection by
opportunistic bacteria like Clostridum difficle.
[0083] Methods for assessing .beta.-glucuronidase activity are
known in the art. See, e.g., Farnleitner et al. (2002) Water Res.
36:975-981; Fior et al. (2009) Plant Sci. 176:130-135; and Szasz
(1967) Clin. Chem. 13:752-759. .beta.-glucuronidase activity of
bacteria provided the selective .beta.-glucuronidase inhibitor can
be reduced by at least about 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%,
45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%,
98%, 99% or 100% when compared to bacteria not provided the
selective .beta.-glucuronidase inhibitor.
[0084] The present invention also provides methods for improving
efficacy of camptothecin-derived antineoplastic agents or
glucuronidase-substrate agents or compounds by attenuating
reactivation by bacterial .beta.-glucuronidases of glucuronidated
metabolites of camptothecin-derived antineoplastic agents or
glucuronidase-substrate agents or compounds. In the methods, a
therapeutically effective amount of at least one selective
.beta.-glucuronidase inhibitor can be administered to a subject
having or about to have treatment with a chemotherapeutic agent,
particularly a camptothecin-derived antineoplastic agent or any
other glucuronidase-substrate agents or compounds.
[0085] As used herein, "subject" means a mammal including but not
limited to a cat, dog, horse, mouse, rat, non-human primate and
human, but preferably a human.
[0086] The therapeutically effective amount of the at least one
selective .beta.-glucuronidase inhibitor can be administered to the
subject prior to, concurrently with or after administration of a
camptothecin-derived antineoplastic agent or
glucuronidase-substrate agent or compound. When the selective
.beta.-glucuronidase inhibitor is administered prior to the
camptothecin-derived antineoplastic agent or
glucuronidase-substrate agent or compound, it can be as a
prophylactic measure. For example, the selective
.beta.-glucuronidase inhibitor can be provided about 2 weeks, 1
week, 6 days, 5 days, 4 days, 3 days, 2 days, 1 day, 12 hours, 10
hours, 8 hours, 6 hours, 5 hours, 4 hours, 3 hours, 2 hours, 1 hour
or even 30 minutes prior to or after the camptothecin-derived
antineoplastic agent or glucuronidase-substrate agent or
compound.
[0087] The compounds and compositions are generally administered
via an oral route. However, any route of administration that will
provide the compounds to the intestine can be used.
[0088] One of skill in the art understands that the effective
amount provided to a subject in need thereof can and will vary
depending upon several clinical parameters. For example, the
therapeutically effective amount of the selective
.beta.-glucuronidase inhibitor will depend on the subject being
treated (e.g., age, weight, sex, etc.), the severity of the
disorder or disease, and the route of administration. Likewise, the
therapeutically effective amount will vary depending upon clinical
and treatment parameters.
[0089] In an embodiment, the subject matter described herein is
directed to the use of a selective .beta.-glucuronidase inhibitor
for the manufacture of a medicament for the use in selectively
inhibiting bacterial .beta.-glucuronidases, for improving
camptothecin-derived antineoplastic agent efficiency, for
attenuating side effects in a subject being administered a
camptothecin-derived antineoplastic agent, for alleviating
gastrointestinal distress associated with chemotherapy, and for
improving the efficiency of a glucuronidase-substrate agent or
compound.
[0090] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
skill in the art to which the invention pertains. Although any
methods and materials similar to or equivalent to those described
herein can be used in the practice or testing of the present
invention, the preferred methods and materials are described
herein.
[0091] The following examples are offered by way of illustration
and not by way of limitation.
EXPERIMENTAL
[0092] Camptothecin, a plant alkaloid derived from the Chinese
Camptotheca acuminata tree, was added to the NCI natural products
screening set in 1966. It showed strong antineoplastic activity but
poor bioavailability and toxic side effects. After thirty years of
modifying the camptothecin scaffold, two derivatives emerged and
are now approved for clinical use. (Pizzolato & Saltz (2003)
Lancet 361:2235-2242). Topotecan (Hycamptin.RTM.; GlaxoSmithKline)
is currently employed to treat solid ovarian, lung and brain
tumors. Id. CPT-11 (also called Irinotecan, and Camptosar.RTM.;
Pfizer) contains a carbamate-linked dipiperidino moiety that
significantly increases bioavailability in mammals. Id. This
dipiperidino group is removed from the CPT-11 prodrug in vivo by
carboxylesterase enzymes that hydrolyze the carbamate linkage to
produce the drug's active metabolite, SN-38. (Smith et al. (2006)
Toxicol In Vitro 20:163-175). CPT-11 is currently used to treat
solid colon, lung and brain tumors, along with refractory forms of
leukemia and lymphoma. (Pommier (2006) Nat Rev Cancer
6:789-802).
[0093] The sole target of the camptothecins is human topoisomerase
I. (Hsiang et al. (1985) J Biol Chem 260:14873-14878). This enzyme
relieves superhelical tension throughout the genome and is
essential for DNA metabolism, including DNA replication,
transcription and homologous recombination. (Redinbo et al. (1999)
Curr Opin Struct Biol 9:29-36). Topoisomerase I breaks one strand
in duplex DNA, forming a covalent 3'-phosphotyrosine linkage, and
guides the relaxation of DNA supercoils. (Redinbo et al. (1998)
Science 279:1504-1513; Stewart et al. (1998) Science
279:1534-1541). It then reseals the single-strand DNA break and
releases a relaxed duplex DNA molecule. The camptothecins bind to
the covalent topoisomerase I-DNA complex and prevent the religation
of the broken single DNA strand, effectively trapping the 91 kDa
protein on the DNA. (Hsiang, 1985). Such immobilized macromolecular
adducts act as roadblocks to the progression of DNA replication and
transcription complexes, causing double-strand DNA breaks and
apoptosis. (Pommier, 2006). Because cancer cells are growing
rapidly, the camptothecins impact neoplastic cells more
significantly than normal human tissues. Structural studies have
established that the camptothecins stack into the duplex DNA,
replacing the base pair adjacent to the covalent phosphotyrosine
linkage. (Chrencik et al. (2004) J Mol Biol 339:773-784; Staker et
al. (2002) Proc Natl Acad Sci USA 99: 15387-15392). Religation of
the nicked DNA strand is prevented by increasing the distance
between the 5'-hydroxyl and the 3'-phosphotyrosine linkage to
>11 .ANG.. Id.
[0094] CPT-11 efficacy is severely limited by delayed diarrhea that
accompanies treatment. (Mathijssen et al. (2001). Clin Cancer Res
7:2182-2194). While an early cholinergic syndrome that generates
diarrhea within hours can be successfully treated with atropine,
the diarrhea that appears .about.2-4 days later is significantly
more debilitating and difficult to control. (Ma & McLeod (2003)
Curr Med Chem 10:41-49). CPT-11 undergoes a complex cycle of
activation and metabolism that directly contributes to drug-induced
diarrhea (FIG. 1A). Id. CPT-11 administered by intravenous
injection can traffic throughout the body, but concentrates in the
liver where it is activated to SN-38 by the human liver
carboxylesterase hCE1 (FIG. 1B). The SN-38 generated in the liver
is eliminated from the body via glucuronidation to SN-38G by the
phase II drug metabolizing UDP-glucuronosyltransferase (UGT)
enzymes (FIG. 1B). (Nagar & Blanchard (2006) Drug Metab Rev
38:393-409). SN-38G is excreted from the liver via the bile duct
and into the GI. Once in the intestines, however, SN-38G serves as
a substrate for bacterial .beta.-glucuronidase enzymes in the
intestinal flora that remove the glucuronide moiety and produce the
active SN-38 (FIGS. 1A-B). (Tobin et al. (2003) Oncol Rep
10:1977-1979). SN-38 in the intestinal lumen produced in this
manner contributes to epithelial cell death and the severe diarrhea
that limits CPT-11 efficacy. This effect has been partially
reversed in rats using the relatively weak (IC.sub.50=90 .mu.M)
.beta.-glucuronidase inhibitor saccharic acid 1,4-lactone. (Fittkau
et al. (2004) J Cancer Res Clin Oncol 130:388-394).
[0095] While broad-spectrum antibiotics have been used to eliminate
enteric bacteria from the gastrointestinal tract prior to CPT-11
treatment (Flieger et al. (2007) Oncology 72:10-16), this approach
has several drawbacks. First, intestinal flora play essential roles
in carbohydrate metabolism, vitamin production, and the processing
of bile acids, sterols and xenobiotics. (Cummings & Macfarlane
(1997) JPEN J Parenter Enteral Nutr 21:357-365; Guarner &
Malagelada (2003) Lancet 361:512-519). Thus, the partial or
complete removal of enteric bacteria is non-ideal for patients
already challenged by neoplastic growths and chemotherapy. Second,
it is well established that the elimination of the symbiotic GI
flora from even healthy patients significantly increases the
chances of infections by pathogenic bacteria, including
enterohemorrhagic E. coli and C. difficile. (Job & Jacobs
(1997) Drug Saf 17:37-46; Levy & Marshall (2004) Nat Med
10:S122-129; Nord et al. (1984) Am J Med 76:99-106; Settle &
Wilcox (1996) Aliment Pharmacol Ther 10:835-841; Sears et al.
(1999) Gastrointest Endosc 50:841-844; Stamp (2004) Med Hypotheses
63:555-556; Yang & Pei (2006) World J Gastroenterol
12:6741-6746). Third, bacterial antibiotic resistance is a human
health crisis, and the unnecessary use of antimicrobials is a
significant contributor to this problem. (Levy & Marshall,
2004).
[0096] .beta.-glucuronidases hydrolyze glucuronic acid sugar
moieties in a variety of compounds. (Basinska & Florianczyk
(2003) Ann Univ Mariae Curie Sklodowska Med 58:386-389). The
presence of .beta.-glucuronidases in a range of bacteria is
exploited in commonly-used water purity tests, in which the
conversion of 4-methylumbelliferyl glucuronide (4-MUG) to
4-methylumbelliferone (4-MU) by .beta.-glucuronidases is assayed to
detect bacterial contamination. (Farnleitner et al. (2002) Water
Res. 36:975-981). While the crystal structure of human
.beta.-glucuronidase was reported in 1996 (Jain et al. (1996) Nat
Struct Biol 3:375-381), no structure of a bacterial
.beta.-glucuronidase has been presented. In addition, whereas
relatively weak inhibitors of .beta.-glucuronidase have been
reported (K.sub.i values of 25 .mu.M to 2 mM) (Russell &
Klaenhammer (2001) Appl Environ Microbiol 67:1253-1261), no potent
and/or selective inhibitors of the bacterial enzymes have been
presented.
Results:
[0097] E. coli .beta.-Glucuronidase Crystal Structure: To
understand bacterial .beta.-glucuronidase activity and inhibition,
we over-expressed, purified and crystallized full-length E. coli
.beta.-glucuronidase in both the apo and inhibitor-bound state for
examination through x-ray diffraction. Native data were collected
to 2.5 .ANG. resolution and data for crystals containing
inhibitor-bound enzyme were collected to 2.4 .ANG. resolution;
however, initial attempts at molecular replacement using the
previously solved human .beta.-glucuronidase model (PDB: 1bhg,
(Jain et al. (1996) Nat Struct Mol Biol 3:375-381)) were
unsuccessful. As such, selenomethionine substituted E. coli
.beta.-glucuronidase was expressed, purified and crystallized to
acquire necessary experimental phases to solve the bacterial
structure. Selenomethionine crystal data were collected to 2.9
.ANG., and experimental phases were acquired using the SAD method.
These phases were used to build the initial model. Molecular
replacement using the SeMet model was utilized on both the native
and inhibitor-bound structure. Data collection and final refinement
statistics are shown in Table 1.
TABLE-US-00001 TABLE 1 Data Collection and Refinement Statistics.
Data Collection X-ray Source APS SER-CAT BM-22 Space group C2 Unit
cell: a, b, c, (.ANG.); .alpha., .beta., 168.9, 77.3, 126.6; 90,
125.0, 90 .gamma. (.degree.) Data set SeMet Native GDL-bound
Wavelength (.ANG.) 0.97926 1.0000 1.0000 Resolution (.ANG.) highest
shell 50.00-2.90 50.0-2.50 50.0-2.40 (3.00-2.90) (2.59-2.50)
(2.49-2.40) 1/.sigma. 22.9 (3.7) 21.9 (2.4) 35.2 (4.1) Completeness
(%) 99.2 (93.7) 96.5 (82.4) 98.6 (93.9) Redundancy 7.4 (6.3) 5.2
(3.3) 7.0 (6.2) Phasing and Refinement Resolution (.ANG.) 50-2.9
50-2.5 50-2.4 No. reflections 26483 43507 50982 Mean figure of
merit 0.74 -- -- R.sub.work 0.253 0.214 0.203 R.sub.free 0.282
0.267 0.254 Molecules per asymmetric 2 2 2 unit (AU) No. of free
amino acids per 1192 1194 1194 AU No. of waters per AU 214 358 355
Average B-factors 48.8 60.5 55.1 R.M.S. deviations Bond lengths
(.ANG.) 0.016 0.003 0.010 Bond angles (.degree.) 2.223 0.815 1.580
Ramachandran (%) Preferred 96.7 97.0 98.4 Allowed 2.7 2.4 1.3
Outliers 0.6 0.6 0.3
[0098] The asymmetric unit in both the native and inhibitor-bound
structures contains two monomers, each composed of 597 ordered
residues (FIG. 2A). Two residues at the C-terminus of the enzyme,
K602 and Q603, lacked electron density, as did a disordered loop
region from 363-369; as such, these regions were not placed in the
final model. The N-terminal domain of E. coli .beta.-glucuronidase
(residues 1-180) contains 12 .beta.-strands and two short
.alpha.-helices, which resembles the sugar binding domain of the
second family of glycosyl hydrolases.sup.30. The C-terminal domain
(274-603) forms an .alpha..beta.-barrel (Jacobson et al. (1994)
Nature 369:761-766) composed of 8 short .beta.-strands and 9
.alpha.-helices, and contains the active site residues E413 and
E504. Between the N- and C-terminal domain (181-273) exists an
immunoglobin-like .beta.-sandwich domain consistent with other
family 2 glycosyl hydrolases containing 7 .beta.-strands. Id. The
three domains of the protein were assigned using BLAST.
(Marchler-Bauer et al. (2009) Nucleic Acids Res 37:D205-210).
Crystallographic symmetry generates the tetramer (FIG. 2B) expected
to be the active form of the enzyme as calculated by gel filtration
(data not shown).
[0099] Superimposing the E. coli .beta.-glucuronidase structure
with the structure of the human enzyme reveals 1.4 .ANG. r.m.s.d.
over 565 equivalent C.alpha. positions (FIG. 5). The E. coli
structure contains one loop of .about.12-17 residues in length not
found in the human structure. Furthermore, the human structure
contains structural elements not seen in the bacterial structure,
including two loops approximately 9-11 residues longer than the
equivalent E. coli loop, and two short helices, which are
unstructured loops in the bacterial structure. In spite of these
differences, the active sites of the bacterial and human enzymes
align well, although in the unliganded E. coli structure a 7-8
residue loop is disordered in the absence of the inhibitor (see
below). Other major differences between the human and E. coli
structures can be seen in solvent-exposed regions, such as loop
residues that shift by 5.6-12.4 .ANG. between the two proteins. An
alignment of the primary .beta.-glucuronidase sequence from E. coli
and Homo sapiens reveal a 45% identity relative to the E. coli
sequence (FIG. 6). In addition, only one residue within 5 .ANG. of
the putative catalytic residues is not conserved between the two
sequences.
[0100] The 2.4 .ANG. resolution glucaro-.delta.-lactam (GDL)-bound
structure reveals a single clear binding mode of the inhibitor
within the .beta.-glucuronidase active site (FIG. 2B). GDL forms
direct contacts with four amino acids (D163, R562, K568, Y472,
H330) and one of the catalytic residues (E413), and is located 2.8
.ANG. from the second catalytic residue, E504 (FIG. 7). The
inhibitor-bound structure shares 1.2 .ANG. r.m.s.d. over 597
equivalent C.alpha. atoms when superimposed on the 2.5 .ANG.
resolution structure of the native, unliganded enzyme. The most
significant site of difference (shifts in backbone position
.gtoreq.2.8 .ANG.) between the two structures occurs at the active
site (FIG. 3A-B). The entrance to the active site in the native
structure is occluded by the 466-476 loop that contains tyrosines
468, 469 and 472, such that this loop would clash sterically with
the observed position of the GDL inhibitor (FIG. 3A). In the
inhibitor-bound structure, this loop has shifted in position to
relocate these aromatic residues 7-14 .ANG. away and allow the GDL
molecule to bind (FIGS. 3A-B). Upon this shift, the open area of
the active site presents itself on the surface of the molecule,
which results in a shift from 10.9 .ANG..sup.2 (unliganded) to 20.8
.ANG..sup.2 (inhibitor-bound) (see FIG. 8), and Y472 forms a direct
contact with the GDL molecule (FIG. 7). Thus, a conformational
change is involved in inhibitor binding to the E. coli
.beta.-glucuronidase active site.
Inhibitors Identification Through High-Throughput Screening:
[0101] To discover novel inhibitors of E. coli
.beta.-glucuronidase, high-throughput screening was conducted using
a 35,000-compound chemical library. A well established
.beta.-glucuronidase assay was also employed, in which the
conversion of 4-methylumbelliferyl-glucuronide (4-MUG) to
4-methylumbelliferone (4-MU) is monitored by measuring the increase
in 4-MU fluorescence (excitation at 365 nm, emission at 450 nm)
(FIG. 9). This assay is widely employed to test water samples for
bacterial contamination. (Farnleitner, 2002). It exhibited robust
characteristics, with a screening Z-score of 0.84. (Zhang et al.
(1999) J Biomol Screen 4:67-73). The hit rate was 0.3% for the 100
compounds that produced 90% inhibition or better, exhibited good
Hill coefficients and R.sup.2 values for inhibition curves of 0.99
or better. Nine compounds representative of the chemical diversity
of the hits were chosen for further investigation (FIG. 4A). It was
noted, however, in considering the chemical structures of these
hits that the potential for absorbance or fluorescence was possible
and may interfere with subsequent characterization in vitro or in
cells. For example, compounds 1-4,6,7 and 9 were found to absorb at
.about.355 nm, close to the excitation wavelength of the 4-MUG
assay (data not shown).
[0102] Thus, two other .beta.-glucuronidase activity assays were
employed to examine the potency of inhibitors both in vitro and in
cell-based studies. An absorbance assay based on the conversion of
p-nitrophenyl glucuronide (PNPG) to p-nitrophenol (PNP) (Szasz
(1967) Clin Chem 13:752-759), which absorbs at 410 nm, was employed
as the primary in vitro assay (FIG. 9). A secondary assay involving
the conversion of phenolphthalein glucuronide (PheG) to
phenolphthalein (Phe), which absorbs at 540 nm, was also employed
(FIG. 9). Id. Both assays were validated in vitro and in living
cells, and the wavelengths monitored did not overlap with
absorbance characteristics of putative inhibitors (data not shown).
Importantly, as outlined below, these assays recapitulated the in
vitro high-throughput screening results obtained with the 4-MUG
substrate. Control experiments were also performed to show that the
enzyme activity detected in cell-based assays was dependent on the
presence of expressed .beta.-glucuronidase. For example, E. coli
cells lacking a .beta.-glucuronidase gene showed no enzyme activity
using PNPG as a substrate; but when a bacterial
.beta.-glucuronidase was expressed in those and wild-type cells
lines, enzyme activity increased accordingly (FIG. 10). The
glucaro-.delta.-lactam (GDL) inhibitor examined in the crystal
structure of E. coli .beta.-glucuronidase exhibited relatively in
vitro weak 1050 values of 45.+-.3.1 .mu.M using PNPG and was
ineffective in cells (FIG. 11).
Potent Inhibition In Vitro and in Living Aerobic and Anaerobic
Bacterial Cells:
[0103] The nine representative compounds chosen from the
high-throughput screening results (FIG. 4A) were all more potent
than glucaro-.delta.-lactam in vitro, and eight of the nine were
effective in living cells as well (Table 2). FIG. 4B shows a
typical graph of the reduction in absorbance representing
decreasing .beta.-glucuronidase activity with an increase of
inhibitor concentration. In vitro, six (1, 2, 4, 5, 8 and 9) of the
nine inhibitors had nanomolar-level IC.sub.50 values, and the other
three (3, 6 and 7) had values of less than 2 .mu.M. Compound 9
proved to be the strongest inhibitor with an IC.sub.50 value of
1.17.+-.0.50 nM (Table 2). Cell-based assays in living E. coli
cells were also conducted on each of the nine compounds; EC.sub.50
values are presented Table 2. The potency of inhibition improved in
cells relative to in vitro for compounds 1, 2, 4, 5, and 7;
however, compounds 6 and 8 showed no improvement, and compound 3
was ineffective. The efficacy of compound 9 remained strong in
cells, with an EC.sub.50 value of 3.58.+-.1.80 nM. To assess the
validity of these results, cell survival was tested in the presence
of 100 .mu.M of each of the nine inhibitors, as well as 1 mM of the
hydrolysis products, PNP and Phe. The nine compounds exhibited no
significant effect on cell survival (FIG. 12). Thus, potent
inhibition of .beta.-glucuronidase activity was achieved in E. coli
cells growing in aerobic conditions.
TABLE-US-00002 TABLE 2 Effect of the Inhibitor Compounds in Two
.beta.-Glucuronidase Assays. In- hibi- PNPG PheG tor IC.sub.50 (nM)
EC.sub.50 (nM) IC.sub.50 (nM) EC.sub.50 (nM) 1 282.5 .+-. 26.05
17.7 .+-. 7.42 277.3 .+-. 30.4 29.0 .+-. 3.33 2 585.7 .+-. 31.1
233.2 .+-. 2.99 600.8 .+-. 55.3 221.2 .+-. 22.01 3 1624 .+-. 1.32
-- 1688.9 .+-. 24.12 -- 4 369.3 .+-. 2.51 28.3 .+-. 2.11 377.8 .+-.
13.71 33.2 .+-. 8.18 5 230.6 .+-. 1.17 92.4 .+-. 1.34 212.6 .+-.
17.9 99.9 .+-. 23.0 6 1058.2 .+-. 3.54 1322.8 .+-. 1.15 1067.2 .+-.
33.2 1302.5 .+-. 15.7 7 1204.6 .+-. 1.70 811 .+-. 1.35 1266.4 .+-.
86.12 913.3 .+-. 20.4 8 740.1 .+-. 20.4 776.9 .+-. 6.44 721.7 .+-.
31.3 793.1 .+-. 27.9 9 1.17 .+-. 0.50 3.58 .+-. 1.80 0.984 .+-.
0.37 3.41 .+-. 1.13
[0104] Because over 99% of the bacterial species present GI tract
are obligate anaerobes (Sears (2005) Anaerobe 11:247-251), E. coli
cells grown under anaerobic conditions were tested, as well as
other relevant anaerobic bacterial species. (Hawksworth et al.
(1971) J Med Microbiol 4:451-459). The cell-based assay using
anaerobic E. coli yielded similar results to those of the aerobic
conditions (FIG. 4C). Furthermore, in-cell assays using the
obligate anaerobe Bacteroides vulgatus also demonstrated inhibitor
efficacy (FIG. 4D). L. reuteri and B. infantis were also tested,
which do not contain the .beta.-glucuronidase gene, (Russell &
Klaenhammer, 2001; Grill et al. (1995) Curr Microbiol 31:23-27) and
found no evidence of enzyme activity or inhibitor impact on assay
signal (data not shown). As such, these cell lines are effective
negative controls. Taken together with the in vitro and cell-based
data outlined above, these results confirm that we have identified
several novel potent inhibitors of .beta.-glucuronidase activity
that are effective in living aerobic and anaerobic bacterial cells
lines but do not impact microbial cell survival.
[0105] With the identification of novel inhibitors of
.beta.-glucuronidase activity, the next step was taken to further
characterize the compounds' effects on human intestinal cells,
similar to those likely to be encountered in the colonic region of
the gastrointestinal tract. HCT116 (Brattain et al. (1981) Cancer
Res 41:1751-1756), human colonic epithelial cells were treated with
each of the nine inhibitors to test the viability of these cells to
grow in their presence. Using the CellQuanti-Blue.TM. Assay Kit,
the HCT116 cells were treated with the inhibitors, and checked for
human cytotoxicity; the results show that the potent inhibitors do
not effect human colonic cells (FIG. 13). The specificity of the
nine compounds was tested by exploring their effects on a mammalian
.beta.-glucuronidase. In vitro assays were conducted using bovine
liver .beta.-glucuronidase in a similar manner to that of the
bacterial enzyme assay. With a range of 0 to 100 .mu.M inhibitor
concentration of each of the nine inhibitors, it was observed that
they have little to no effect on the activity of this mammalian
.beta.-glucuronidase (FIG. 4B).
Discussion:
[0106] The first crystal structure of a bacterial
.beta.-glucuronidase enzyme is reported herein, as well as
structures of both the unliganded protein and complexed with an
inhibitor. A significant shift in the position of an active site
loop upon ligand binding reveals that conformational change may be
involved in the formation of all substrate and inhibitor complexes
with the enzyme (e.g., FIG. 3B). The residues on this loop (466-474
and 503-505) are nearly fully conserved between the bacterial and
human .beta.-glucuronidases; thus, a similar "induced fit"
mechanism may be at play in eukaryotic .beta.-glucuronidases as
well. Importantly, knowledge of the changes in structure that can
occur at the bacterial .beta.-glucuronidase active site can be
employed in the in silico screening and validation of additional
potential enzyme inhibitors. In addition, the binding of SN-38G
(see FIG. 1) and compound 9 (see FIG. 4A) into the
.beta.-glucuronidase active site (FIGS. 14A-B) were modeled.
Several critical interactions are formed between conserved
catalytic gorge residues on the enzyme (e.g., Y468, Y472, N466, and
D163) and functional groups on the substrate and inhibitor.
Additionally, both compounds take on a curved shaped, allowing them
to fit tightly into the curved tunnel of the active site. These
models provide a useful place to begin to develop improved
inhibitors by structure-based design.
[0107] The nine compounds that were characterize further from the
300 plus hits from high-throughput screening all are effective
inhibitors of the .beta.-glucuronidase enzyme in vitro (with
IC.sub.50s of 1 nM-1.6 .mu.M), and eight of the nine maintain 3
nM-1.3 .mu.M efficacy in living bacterial cells. Furthermore, they
exhibit .beta.-glucuronidase inhibition in anaerobic conditions and
against an obligate anaerobe, Bacteroides vulgatus, known to be a
significant component of the human gastrointestinal microflora.
(Sears, 2005). Importantly, however, the inhibitors characterized
here do not impact bacterial cell growth or survival. This was a
desired characteristic of compounds designed to be used in
conjunction with CPT-11. Effective .beta.-glucuronidase inhibitors
would reduce SN-38 reactivation in the GI without eliminating these
commensal bacteria that promote health and prevent infection by
opportunistic bacteria like Clostridium difficile. (Guarner &
Malagelada 2003; Job & Jacobs, 1997).
[0108] In medicinal applications, these potent inhibitors can
contact the human epithelial cell lining in the intestine. HCT116
human colonic epithelial cells were incubated with the nine
compounds in order to test them for cytotoxic effects on mammalian
cells. As shown (FIG. 13), the inhibitors have little to no
cytotoxicity, and these cells continue to be viable in their
presence. As such, novel potent inhibitors have been discovered
that not only inhibit .beta.-glucuronidase in vivo, but are also
non-toxic to bacterial cells lines, anaerobic and aerobic, as well
as human epithelial cells known to inhabit the GI tract. This is a
crucial starting point to move into more clinical settings.
[0109] To assess the selectivity of the nine compounds a mammalian
.beta.-glucuronidase, from bovine liver, was incubated and tested
for enzyme activity in their presence. The nine compounds appear to
not inhibit this mammalian enzyme as they do the bacterial (data
not shown, see FIG. 4B for example). These results suggest that the
inhibitors show a fair amount of selectivity towards the bacterial
enzyme. Preliminary analysis via sequence and structural alignment
(see FIGS. 5-6) indicates that the .about.12 residue loop (362-374)
in the E. coli .beta.-glucuronidase that hovers over the active
site opening, of which is missing in the human enzyme (bovine liver
.beta.-glucuronidase is 82% identical and is also missing this loop
region), may play a part in this issue. The major role of the
mammalian version of the enzyme is to cleave the glucuronic acid
moiety from long chain glycosaminoglycans. (Ray et al. (1999) J
Hered 90:119-123; Eudes et al. (2008) Plant Cell Physiol
49:1331-1341). As such, these enzymes must have the ability to
accommodate these large substrates. The lack of this loop region
would allow for a more open active site and avenue for larger
substrates to reside. This loop region, which is present in the
bacterial enzyme, would suggest that small molecules, such as
glucuronide linked xenobiotics (Eudes, 2008) would have a tighter
fit in the active site such that the enzyme would be turned "off"
more frequently.
[0110] CPT-11 is currently used largely in combination with a
number of well-known chemotherapeutics (Masuda et al. J Clin Oncol
10:1775-1780; Saltz et al. (1996) Eur J Cancer 32A Suppl 3:S24-31)
but can still be employed as a single agent in colorectal cancer.
(Armand et al. (1995) Eur J Cancer 31A:1283-1287; Shimada et al.
(1996) Eur J Cancer 32A Suppl 3:S13-17). To improve the outcome for
subject on CPT-11 alone, and potentially to allow more single agent
use, one can reduce the diarrhea that limits dose intensification
and efficacy. An approach can be to inhibit the
.beta.-glucuronidase enzyme known to reactivate SN-38G to SN-38 in
the lower gastrointestinal tract. Such inhibitors are potent and
effective in living bacterial cells, but do not kill the bacteria
that inhabit the gastrointestinal tract.
Materials and Methods:
[0111] Expression and Purification of E. coli .beta.-Glucuronidase.
The full-length E. coli .beta.-glucuronidase gene was obtained from
genomic DNA and was cloned into the pET-28a expression plasmid
(Novagen) with an N-terminal 6.times.-Histidine tag. BL21-DE3
competent cells were transformed with the expression plasmid and
grown in the presence of kanamycin (25 ug/ml) in LB medium with
vigorous shaking at 37.degree. C. The expression was induced with
the addition of 0.3 mM IPTG and further incubated for 4 hours.
Cells were centrifuged at 4500.times.g for 20 min at 4.degree. C.
for collection. Cell pellets were resuspended in Buffer A, along
with PMSF and protease inhibitors containing aprotinin and
leupeptin. Resuspended cells were lysed by sonication and clarified
by centrifugation. Protein was purified by Ni-chromatography column
followed by gel filtration.
Selenomethionine Substituted .beta.-Glucuronidase.
[0112] B834 competent cells were transformed with pET-28a
containing the .beta.-glucuronidase gene. SelenoMet.TM. Medium and
Nutrient Mix (AthenaES) were prepared for growth, with 50 mg of
selenomethionine added for each liter of medium. The cells were
grown and induced the same as the native .beta.-glucuronidase. The
temperature was lowered to 15.degree. C. and the cultures grown
overnight with shaking.
Crystallization, Data Collection, and Phasing.
[0113] Crystals were obtained at 2 mg/mL protein in 15% PEG3350,
0.2 M Magnesium Acetate, and 0.02% Sodium Azide at 16.degree. C.
Crystals were cryo-protected with perfluoropolyether oil (Sigma)
and flash cooled in liquid nitrogen. Diffraction data were
collected on the 22-BM beam line at SER-CAT (Advanced Photon
Source, Argonne National Laboratory). Data were indexed and scaled
using HKL2000. (Otwinowski et al., "Processing of X-ray diffraction
data collected in oscillation mode" 307-326 In: Methods in
Enzymology, Vol. 276 (Academic Press 1997)). Selenomethionine data
were collected to 2.9 .ANG. and processed similarly. The PHENIX
software suite was utilized to locate heavy atom sites and to trace
a portion of the model. (Adams et al. (2002) Acta Crystallogr D
Biol Crystallogr 58:1948-1954). An initial model was built in Coot
using the SAD data and used with Phaser for molecular replacement.
(Emsley & Cowtan (2004) Acta Crystallogr D Biol Crystallogr
60:2126-2132; McCoy et al. (2007) J Appl Crystallogr 40:658-674).
The structure was refined using simulated annealing and torsion
angle refinement in CNS, and monitored using both the
crystallographic R and cross-validating R-free statistics. (Brunger
(1997) Methods Enzymol 277:366-396). Data collection and refinement
statistics are presented in Table 1. PHENIX was used for
anisotropic B-factor and TLS refinement. (Adams, 2002). The model
was manually adjusted using Coot and 2F.sub.o-F.sub.c and
F.sub.o-F.sub.c electron density maps. The GDL model and definition
files were generated using PRODRG. (Schuttelkopf & van Aalten
(2004) Acta Crystallogr D Biol Crystallogr 60:1355-1363).
Inhibitor Compounds.
[0114] Purified protein was sent to NCCU-BRITE to screen various
compound libraries for potential inhibitors. Nine compounds were
chosen for further analysis. The compounds (FIG. 4A) were purchased
from ASINEX. Each compound was provided as a solid powder and
dissolved in 100% DMSO.
In Vitro .beta.-Glucuronidase Assays.
[0115] In vitro assays were conducted at 50 .mu.L total volume in
96-well, clear bottom assay plates (Costar). Substrates consisted
of PNPG or PheG (FIG. 9) and were acquired from Sigma. The presence
of the hydrolysis product of each, PNP or Phe, was measured by
absorbance at 410 nm or 540 nm, respectively. Reactions were
allowed to proceed for 6 hours at 37.degree. C. and were quenched
with 100 .mu.L of 0.2 M sodium carbonate. Absorbance was measured
using a PHERAstar Plus microplate reader (BMG Labtech).
Human Cell Survivability.
[0116] The nine compounds were tested for cytotoxicity in human
cells. HCT116 human epithelial colonic cells were grown and
cultured in DMEM medium till confluent and adherent. Cells were
counted and dilutions were made to achieve a 50,000 cell count per
reaction.
Mammalian .beta.-Glucuronidase In Vitro Assays.
[0117] Bovine liver .beta.-glucuronidase was acquired in
lyophilized form from Sigma. The protein was dissolved and the
assay was conducted as previously published, using PNPG as the
substrate for activity detection. (Graef et al. (1977) Clin Chem
23:532-535). Each inhibitor was tested for an effect on mammalian
.beta.-glucuronidase activity. Reaction time and temperature were
the same as previously described (see In Vitro .beta.-Glucuronidase
Assays).
Cell-Based Inhibition Assays.
[0118] HB101 E. coli cells were grown to an OD.sub.600 of 0.6 in LB
medium. These cells were then used for an in vivo assay. Reaction
time and temperature were the same as previously described (see In
Vitro .beta.-Glucuronidase Assays). The .beta.-glucuronidase gene
(GUS) knockout cell-line (GMS407) was purchased from CGSC at Yale
University. Absorbance was measured at the appropriate wavelength,
depending on the substrate. Cell survivability in the presence of
the nine inhibitors was tested by plating cells with each
compound.
Anaerobic In Vivo Studies.
[0119] Lactobacillus reuteri, Bifidobacterium infantis, Bacteroides
vulgatus and Clostridium ramosum were provided by the Sartor Lab at
the University of North Carolina at Chapel Hill. Anaerobic bacteria
were plated on MRS and BHI plates. Prior to streaking, plates were
pre-equilibrated in an anaerobic chamber using the BD BBL.TM.
GasPak.TM. Plus Anaerobic System Envelopes.
Supplemental Methods:
[0120] Expression and Purification of E. coli .beta.-Glucuronidase.
The full-length E. coli .beta.-glucuronidase gene was obtained from
bacterial genomic DNA and was cloned into the pET-28a expression
plasmid (Novagen) with an N-terminal 6.times.-Histidine tag.
BL21-DE3 competent cells were transformed with the expression
plasmid and grown in the presence of kanamycin (25 ug/ml) in LB
medium with vigorous shaking at 37.degree. C. until an OD.sub.600
of 0.6 was attained. The expression was induced with the addition
of 0.3 mM isopropyl-1-thio-D-galactopyranoside (IPTG) and further
incubated at 37.degree. C. for 4 hours. Cells were collected by
centrifugation at 4500.times.g for 20 min at 4.degree. C. in a
Sorvall (model RC-3B) swinging bucket centrifuge. Cell pellets were
resuspended in Buffer A (20 mM Potassium Phosphate, pH 7.4, 25 mM
Imidazole, 500 mM NaCl), along with PMSF (2 .mu.L/mL from 100 mM
stock) and 0.05 .mu.L/mL of protease inhibitors containing 1 mg/mL
of aprotinin and leupeptin. Resuspended cells were sonicated and
centrifuged at 14,500.times.g for 30 min in a Sorvall (model RC-5B)
centrifuge to clarify the lysate. The cell lysate was flowed over a
pre-formed Ni-NTA His-Trap gravity column and washed with Buffer A.
The Ni-bound protein was eluted with Buffer B (20 mM Potassium
Phosphate, pH 7.4, 500 mM Imidazole, 500 mM NaCl). Collected
fractions were then tested for initial purity by SDS-PAGE.
Relatively pure (.about.85%) fractions were combined and loaded
into the Aktaxpress FPLC system (Amersham Biosciences) and passed
over a HiLoad.TM. 16/60 Superdex.TM. 200 gel filtration column. The
protein was eluted into 20 mM HEPES, pH 7.4, and 50 mM NaCl for
crystallization and activity assays. Two milliliter fractions were
collected based on highest ultraviolet absorbance at 280 nm.
Fractions were analyzed by SDS-PAGE (which indicated >95%
purity), combined, and concentrated to 10 mg/mL for long-term
storage at -80.degree. C.
Selenomethionine Substituted .beta.-Glucuronidase.
[0121] To express selenomethionine-substitued enzyme, B834
competent cells were transformed with pET-28a containing the
.beta.-glucuronidase gene. SelenoMet.TM. Medium and Nutrient Mix
(AthenaES) was prepared for growth, with 50 mg of selenomethionine
added for each liter of medium. The cells were grown at 37.degree.
C. until an OD.sub.600 of 0.6 was reached and then were induced
with 0.3 mM IPTG. The temperature was lowered to 15.degree. C. and
the cultures were grown overnight with shaking. Purification was
performed as for the wild-type enzyme (see above).
Crystallization, Data Collection, and Phasing.
[0122] Crystals of E. coli .beta.-glucuronidase were obtained at 2
mg/mL protein in 15% PEG3350, 0.2 M Magnesium Acetate, and 0.02%
Sodium Azide at 16.degree. C. Crystals first appeared after 5 days,
and grew to a final size of approximately 100.times.100.times.50
.mu.m. (Pommier, 2006). Crystals were cryo-protected with
perfluoropolyether vacuum pump oil (Sigma) and flash cooled in
liquid nitrogen. Diffraction data were collected on the 22-BM beam
line at SER-CAT (Advanced Photon Source, Argonne National
Laboratory). Data was indexed and scaled using HKL2000. The
crystals exhibited a space group C2, and the asymmetric unit
contained two monomers. Selenomethionine data were collected to 2.9
.ANG. and processed similarly. The PHENIX software suite (AutoSol)
was utilized to locate heavy atom sites and to trace a portion of
the model. An initial model was built by hand in Coot using the SAD
data and later used with Phaser for molecular replacement with a
native data set and the inhibitor bound structure. The structure
was refined using simulated annealing and torsion angle refinement
with the maximum likelihood function target in CNS, and monitored
using both the crystallographic R and cross-validating R-free
statistics. Data collection and refinement statistics are presented
in Table 1. The software suite PHENIX was used for anisotropic
B-factor and TLS refinement. The model was manually adjusted using
Coot and 2F.sub.o-F.sub.c and F.sub.o-F.sub.c electron density
maps. The glucaro-.delta.-lactam model and definition files were
generated using PRODRG, and after a ligand search using Coot, was
easily placed into electron density in the active site of both
monomers.
Inhibitor Compounds.
[0123] Purified protein was sent to NCCU-BRITE to screen various
compound libraries for potential inhibitors. Nine compounds were
chosen for further analysis. The compounds (FIG. 3A) were purchased
from ASINEX. Each compound was provided as a solid powder and
dissolved in 100% dimethyl sulfoxide (DMSO) to various
concentrations.
In Vitro .beta.-Glucuronidase Assays.
[0124] In vitro assays were conducted at 50 .mu.L total volume in
96-well, clear bottom assay plates (Costar). Reactions consisted of
the following: ten microliters Assay Buffer (5 .mu.L of 5% DMSO,
and 5 .mu.L of 500 mM HEPES, pH 7.4), 30 .mu.L substrate (various
concentrations), 5 .mu.L of an inhibitor solution (various
concentrations), and 5 .mu.L of 5 nM enzyme. Substrates used
consisted of p-nitrophenyl glucuronide (PNPG) and phenolphthalein
glucuronide (PheG) (FIG. 8) and were acquired from Sigma. The
presence of the hydrolysis product of each, p-nitrophenol (PNP) and
phenolphthalein (Phe), was measured by absorbance at 410 nm or 540
nm, respectively. Reactions were allowed to proceed for 6 hours at
37.degree. C. and were quenched with 100 .mu.L of 0.2 M sodium
carbonate. Absorbance was measured using a PHERAstar Plus
microplate reader (BMG Labtech). Data acquired was analyzed using
Microsoft Excel and Sigmaplot 11.0.
Human Cell Survivability.
[0125] The nine compounds were tested for cytotoxicity in human
cells. HCT116 human epithelial colonic cells were grown and
cultured in DMEM medium till confluent and adherent. Cells were
counted and the appropriate dilutions were made to achieve a 50,000
cell count per reaction. The HCT116 cells were aliquoted onto a
96-well assay plate and allowed to incubate at 37.degree. C. in
media for 16 hours prior to treatment with inhibitors. After
incubation, 1 .mu.L of each inhibitor, to achieve a final
concentration of 100 .mu.M, were added to the cells and further
incubated for 6 hours. Using the CellQuanti-Blue.TM. Cell Viability
Assay Kit (BioAssay Systems), 10 .mu.L of the CellQuanti-Blue.TM.
Reagent was added to each reaction and incubated at 37.degree. C.
for 2 hours. After incubation with the reagent, fluorescence was
measured with excitation at 544 nm and emission at 590 nm.
Mammalian .beta.-Glucuronidase In Vitro Assays.
[0126] Bovine liver .beta.-glucuronidase was acquired in
lyophilized form from Sigma. The protein was dissolved and the
assay was conducted as previously published, using PNPG as the
primary substrate for enzyme activity detection. The reaction
mixture contained 1 .mu.M bovine liver .beta.-glucuronidase and 1
mM PNPG substrate. Each of the nine inhibitors were tested for an
effect on mammalian .beta.-glucuronidase activity by adding a
concentration range of 0 to 100 .mu.M to the reaction mixture. The
reaction was allowed to proceed for 6 hours and then quenched with
0.2 M Sodium Carbonate. Absorbance was measured at the appropriate
wavelength, and the data analyzed using Microsoft Excel and
SigmaPlot 11.0.
Cell-Based Inhibition Assays.
[0127] HB101 E. coli cells, transformed with the pET-28a vector
containing the .beta.-Glucuronidase gene, were grown to an
OD.sub.600 of 0.6 in LB medium. The cells were then used in the in
vivo assays to assess the glucuronidase activity and efficacy of
the inhibitors. This assay was performed in a similar manner to the
in vitro assay: ten microliters of substrate, 1 .mu.L of inhibitor
solution, and 40 .mu.L of cells. Again, after 6 hours of incubation
at 37.degree. C., the reaction was quenched with 100 .mu.L of 0.2 M
Sodium Carbonate. A .beta.-glucuronidase gene (GUS) knockout
cell-line (GMS407) was purchased from CGSC at Yale University.
Absorbance was measured at the appropriate wavelength, either 410
nm or 540 nm. Cell survivability in the presence of the nine
inhibitors was assessed by plating a 10.sup.-5 dilution of 200
.mu.L of saturated cells after incubation with 100 .mu.M of each
inhibitor for 6 hours. In addition, 1 mM of each hydrolysis
product, 10 nM Tetracycline, and 2% DMSO (maximum concentration of
DMSO when 100 .mu.M inhibitor is added) were also tested for
inhibitor effects on cell growth. Plated cells were allowed to
incubate at 37.degree. C. overnight, and colonies were counted to
quantify the viability of the cells.
Anaerobic In Vivo Studies.
[0128] For the anaerobic cell lines used, two types of growth
medium and agar plates were prepared: MRS medium/agar was used for
Lactobacillus reuteri and Bifidobacterium infantis, and BHI
medium/agar for Bacteroides vulgatus and Clostridium ramosum.
Anaerobic cell lines were graciously provided by the Sartor Lab at
the University of North Carolina at Chapel Hill. MRS agar plates
were prepared by combining MRS and agar powder, as well as 0.1 g
L-cysteine. BHI plates were produced in a similar manner with the
addition of 0.2 mL each of 5 mg/mL hemin and 0.1% resazurin. Prior
to streaking, plates were pre-equilibrated in an oxygen-free
environment created in an anaerobic chamber and using the BD
BBL.TM. GasPak.TM. Plus Anaerobic System Envelopes. One day before
an assay was conducted, 5 mL overnight cultures, using the
appropriate medium, were grown with no antibiotic present. Assay
plates were prepared similar to the E. coli cell studies, and the
reaction was allowed to progress in the anaerobic chamber for 6
hours. Absorbance data was collected after the reaction was
quenched and analyzed.
[0129] All publications and patent applications mentioned in the
specification are indicative of the level of those skilled in the
art to which this invention pertains. All publications and patent
applications are herein incorporated by reference to the same
extent as if each individual publication or patent application was
specifically and individually indicated to be incorporated by
reference.
[0130] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
of understanding, it will be obvious that certain changes and
modifications may be practiced within the scope of the appended
claims.
Sequence CWU 1
1
21603PRTEscherichia coli 1His Leu Arg Pro Val Glu Thr Pro Thr Arg
Glu Ile Lys Lys Leu Asp1 5 10 15Gly Leu Trp Ala Phe Ser Leu Asp Arg
Glu Asn Cys Gly Ile Asp Gln 20 25 30Arg Trp Trp Glu Ser Ala Leu Gln
Glu Ser Arg Ala Ile Ala Val Pro 35 40 45Gly Ser Phe Asn Asp Gln Phe
Ala Asp Ala Asp Ile Arg Asn Tyr Val 50 55 60Gly Asn Val Trp Tyr Gln
Arg Glu Val Phe Ile Pro Lys Gly Trp Ala65 70 75 80Gly Gln Arg Ile
Val Leu Arg Phe Asp Ala Val Thr His Tyr Gly Lys 85 90 95Val Trp Val
Asn Asn Gln Glu Val His Glu His Gln Gly Gly Tyr Thr 100 105 110Pro
Phe Glu Ala Asp Val Thr Pro Tyr Val Ile Ala Gly Lys Ser Val 115 120
125Arg Ile Thr Val Cys Val Asn Asn Glu Leu Asn Trp Gln Thr Ile Pro
130 135 140Pro Gly His Val Ile Thr Asp Glu Asn Gly Lys Lys Lys Gln
Ser Tyr145 150 155 160Phe His Asp Phe Phe Asn Tyr Ala Gly Ile His
Arg Ser Val His Leu 165 170 175Tyr Thr Thr Pro Asn Thr Trp Val Asp
Asp Ile Thr Val Val Thr His 180 185 190Val Ala Gln Asp Cys Asn His
Ala Ser Val Asp Trp Gln Val Gly Ala 195 200 205Asn Gly Asp Val Ser
Val Glu Leu Arg Asp Ala Asp Gln Gln Val Val 210 215 220Ala Thr Gly
Gln Gly Thr Ser Gly Thr Leu Gln Val Val Asn Pro His225 230 235
240Leu Trp Gln Pro Gly Glu Gly Tyr Leu Tyr Glu Leu Cys Val Thr Ala
245 250 255Lys Ser Gln Thr Glu Cys Asp Ile Tyr Leu Leu Arg Val Gly
Ile Arg 260 265 270Ser Val Ala Val Lys Gly Glu Gln Phe Leu Ile Asn
His Lys Pro Phe 275 280 285Tyr Phe Thr Gly Phe Gly Arg His Glu Asp
Ala Asp Leu Arg Gly Lys 290 295 300Gly Phe Asp Asn Val Leu His Val
His Asp His Ala Leu His Asp Trp305 310 315 320Ile Gly Ala Asn Ser
Tyr Arg Thr Ser His Tyr Pro Tyr Ala Glu Glu 325 330 335His Leu Asp
Trp Ala Asp Glu His Gly Ile Val Val Ile Asp Glu Thr 340 345 350Ala
Ala Val Gly Phe Asn Leu Ser Leu Gly Ile Gly Phe Glu Ala Gly 355 360
365Asn Lys Pro Lys Glu Leu Tyr Ser Glu Glu Ala Val Asn Gly Glu Thr
370 375 380Gln Gln Ala His Leu Gln Ala Ile Lys Glu Leu Ile Ala Arg
Asp Lys385 390 395 400Asn His Pro Ser Val Val His Trp Ser Ile Ala
Asn Glu Pro Asp Thr 405 410 415Arg Pro Gln Gly Ala Arg Glu Tyr Phe
Ala Pro Leu Ala Glu Ala Thr 420 425 430Arg Lys Leu Asp Pro Thr Arg
Pro Ile Thr Cys Val Asn Val His Phe 435 440 445Cys Asp Ala His Thr
Asp Thr Ile Ser Asp Leu Phe Asp Val Leu Cys 450 455 460Leu Asn Arg
Tyr Tyr Gly Trp Tyr Val Gln Ser Gly Asp Leu Glu Thr465 470 475
480Ala Glu Lys Val Leu Glu Lys Glu Leu Leu Ala Trp Gln Glu Lys Leu
485 490 495His Gln Pro Ile Ile Ile Thr Glu Tyr Gly Val Asp Thr Leu
Ala Gly 500 505 510Leu His Ser His Tyr Thr Asp His Trp Ser Glu Glu
Tyr Gln Cys Ala 515 520 525Trp Leu Asp His Tyr His Arg Val Phe Asp
Arg Val Ser Ala Val Val 530 535 540Gly Glu Gln Val Trp Asn Phe Ala
Asp Phe Ala Thr Ser Gln Gly Ile545 550 555 560Leu Arg Val Gly Gly
Asn Lys Lys Gly Ile Phe Thr Arg Asp Arg Lys 565 570 575Pro Lys Ser
Ala Ala Phe Leu Leu Gln Lys Arg Trp Thr Gly His Asn 580 585 590Phe
Gly Glu Lys Pro Gln Gln Gly Gly Lys Gln 595 6002613PRTHomo sapiens
2Leu Gly Leu Gln Gly Gly His Leu Tyr Pro Gln Glu Ser Pro Ser Arg1 5
10 15Glu Cys Lys Glu Leu Asp Gly Leu Trp Ser Phe Arg Ala Asp Phe
Ser 20 25 30Asp Asn Arg Arg Arg Gly Phe Glu Glu Gln Trp Tyr Arg Arg
Pro Leu 35 40 45Trp Glu Ser Gly Pro Thr Val Asp His Pro Val Pro Ser
Ser Phe Asn 50 55 60Asp Ile Ser Gln Asp Trp Arg Leu Arg His Phe Val
Gly Trp Val Trp65 70 75 80Tyr Glu Arg Glu Val Ile Leu Pro Glu Arg
Trp Thr Gln Asp Leu Arg 85 90 95Thr Arg Val Val Leu Arg Ile Gly Ser
Ala His Ser Tyr Ala Ile Val 100 105 110Trp Val Asn Gly Val Asp Thr
Leu Glu His Glu Gly Gly Tyr Leu Pro 115 120 125Phe Glu Ala Asp Ile
Ser Asn Leu Val Gln Val Gly Pro Leu Pro Ser 130 135 140Arg Leu Arg
Ile Thr Ile Ala Ile Asn Asn Thr Leu Thr Pro Thr Thr145 150 155
160Leu Pro Pro Gly Thr Ile Gln Tyr Leu Thr Asp Thr Ser Lys Tyr Pro
165 170 175Lys Gly Tyr Phe Val Gln Asn Thr Tyr Phe Asp Phe Phe Asn
Tyr Ala 180 185 190Gly Leu Gln Arg Ser Val Leu Leu Tyr Thr Thr Pro
Thr Thr Tyr Ile 195 200 205Asp Asp Ile Thr Val Thr Thr Ser Val Glu
Gln Asp Ser Gly Leu Val 210 215 220Asn Tyr Gln Ile Ser Val Lys Gly
Ser Asn Leu Phe Lys Leu Glu Val225 230 235 240Arg Leu Leu Asp Ala
Glu Asn Lys Val Val Ala Asn Gly Thr Gly Thr 245 250 255Gln Gly Gln
Leu Lys Val Pro Gly Val Ser Leu Trp Trp Pro Tyr Leu 260 265 270His
His Glu Arg Pro Ala Tyr Leu Tyr Ser Leu Glu Val Gln Leu Thr 275 280
285Ala Gln Thr Ser Leu Gly Pro Val Ser Asp Phe Tyr Thr Leu Pro Val
290 295 300Gly Ile Arg Thr Val Ala Val Thr Lys Ser Gln Phe Leu Ile
Asn Gly305 310 315 320Lys Pro Phe Tyr Phe His Gly Val Asn Lys His
Glu Asp Ala Asp Ile 325 330 335Arg Gly Lys Gly Phe Asp Trp Pro Leu
Leu Val Lys Asp Phe Asn Leu 340 345 350Leu Arg Trp Leu Gly Ala Asn
Ala Phe Arg Thr Ser His Tyr Pro Tyr 355 360 365Ala Glu Glu Val His
Gln His Cys Asp Arg Tyr Gly Ile Val Val Ile 370 375 380Asp Glu Cys
Pro Gly Val Gly Leu Ala Leu Pro Gln Phe Phe Asn Asn385 390 395
400Val Ser Leu His His His His Gln Val His Glu Glu Val Val Arg Arg
405 410 415Asp Lys Asn His Pro Ala Val Val His Trp Ser Val Ala Asn
Glu Pro 420 425 430Ala Ser His Leu Glu Ser Ala Gly Tyr Tyr Leu Lys
His Val Ile Ala 435 440 445His Thr Lys Ser Leu Asp Pro Ser Arg Pro
Val Thr Phe Val Ser Asn 450 455 460Ser Asn Tyr Ala Ala Asp Lys Gly
Ala Pro Tyr Val Asp Val Ile Cys465 470 475 480Leu Asn Ser Tyr Tyr
Ser Trp Tyr His Asp Tyr Gly His Leu Glu Leu 485 490 495Ile Gln Leu
Gln Leu Ala Thr Gln Phe Glu Asn Trp Tyr Lys Lys Tyr 500 505 510Gln
Lys Pro Ile Ile Gln Ser Glu Tyr Gly Ala Glu Thr Ile Ala Gly 515 520
525Phe His Gln Asp Pro Pro Leu His Phe Thr Glu Glu Tyr Gln Lys Ser
530 535 540Leu Leu Glu Gln Tyr His Leu Gly Leu Asp Gln Lys Arg Arg
Lys Tyr545 550 555 560Val Val Gly Glu Leu Ile Trp Asn Phe Ala Asp
Phe His Thr Glu Gln 565 570 575Ser Pro Thr Arg Val Leu Gly Asn Lys
Lys Gly Ile Phe Thr Arg Gln 580 585 590Arg Gln Pro Lys Ser Ala Ala
Phe Leu Leu Arg Glu Arg Tyr Trp Lys 595 600 605Ile Ala Asn Glu Thr
610
* * * * *